Experimental Study On Bonding Properties Of CFRP-wood Interface

Carbon fiber reinforced polymer(CFRP)is widely used in the reinforcement of existing structures due to its advantages of light weight,small size,high strength,large geometric plasticity,easy cutting and molding,easy construction,and good corrosion resistance and fire resistance,especially in the protection of ancient cultural relics.The CFRP-wood structure realizes the load transfer between the two materials through the bonding force between the CFRP and the wood interface,so that the two materials are combined together to work together.Therefore,the bonding performance of the CFRP-wood interface is the key to study the technology of externally bonded CFRP-wood structure.The effective bond length,interfacial bond shear stress-slip relationship model and bond bearing capacity model are the important theoretical basis and practical reference to guide the CFRP reinforced wood structure.At present,the research on the mechanical properties of CFRP-wood structure interface is still insufficient.In order to study the influence of different factors on the mechanical properties of bond interface,this paper analyzes the development law of CFRP plate strain and interfacial bond shear stress through the double shear test of CFRP-wood specimens,and discusses the influence of CFRP paste length and width on the interfacial bond performance.At the same time,the concept of wood surface damage rate was introduced to study the influence of wood surface damage on the mechanical properties of CFRP-wood interface,and the interface bond bearing capacity model considering initial damage was established.Through the finite element software ABAQUS,the mechanical properties of CFRP-wood interface were modeled and analyzed,and the transfer law of interface stress was further explored.The main research contents and conclusions of this paper are as follows:(1)The experimental study on the composition materials(CFRP,Pinus sylvestris var.mongolica,impregnating resin)of CFRP-wood interface was carried out,and the failure modes of CFRP cloth,impregnating resin and wood were analyzed to obtain the main physical and mechanical properties of different materials.(2)The failure of CFRP-wood interface is mainly the shallow shear failure(brittle failure)of wood matrix;the interface bearing capacity is positively correlated with the bond width of CFRP.When the bond length of CFRP is less than the effective bond length,the interface bearing capacity increases with the increase of the bond length of CFRP.When the bond length of CFRP is greater than the effective bond length,the interface bearing capacity almost no longer increases,but the ductility of the interface increases.(3)On the basis of the existing theoretical model,a modified model of interfacial bond capacity was established by comparing and analyzing the experimental results,and the predicted values of the model were basically consistent with the experimental values.Through the force analysis of the micro-section of the bond interface and the regression analysis of the test results,the calculation expressions of the CFRP strain and the interfacial shear stress distribution in the whole loading process are given,and the interfacial bond shear stress-slip model is obtained.The model prediction curve is in good agreement with the test curve.(4)The initial damage of the wood surface destroyed the integrity of the wood surface fiber,making the ultimate bearing capacity of the interface decrease with the increase of the damage rate,and the brittle characteristics of the interface obvious.Through the analysis and fitting of the experimental data,a model of interfacial bond bearing capacity considering the initial damage of wood surface was established.The error between the calculated results and the experimental values was less than 6 %.(5)The finite element software was used to simulate the CFRP-wood interface.The simulation results show that the interfacial bonding shear stress is a process of transfer from the loading end to the free end,which is consistent with the experimental results.At the same time,the interface ultimate bearing capacity predicted by numerical simulation is in good agreement with the experimental results.